using System;
using System.Linq;

namespace CondenseArrayToNumber
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] num = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int agentLength = 1;

            int[] alpha = new int[num.Length + 2];
            for (int i = 0; i < num.Length; i++)
            {
                alpha[i] = num[i];
            }
            while (agentLength < num.Length)
            {
                for (int i = 0; i < alpha.Length - 1; i++)
                {
                     alpha[i] = alpha[i] + alpha[i + 1];
                }
                agentLength++;
            }
            Console.WriteLine(alpha[0]);
        }
    }
}